1. Field of the Invention
This invention relates to polishing apparatus, in particular to a conditioning and cleaning apparatus for use during chemical mechanical polishing of a semiconductor wafer.
2. Description of Related Art
Fabrication of semiconductor integrated circuits (IC) is a complicated multi-step process for creating microscopic structures with various electrical properties to form a connected set of devices. As the level of integration of IC's increases, the devices become smaller and more densely packed, requiring more levels of photolithography and more processing steps. As more layers are built up on the silicon wafer, problems caused by surface non-planarity become increasingly severe and can impact yield and chip performance. During the fabrication process, it may become necessary to remove excess material in a process referred to as planarization.
A common technique used to planarize the surface of a silicon wafer is chemical mechanical polishing (CMP). CMP involves the use of a polishing pad affixed to a circular polishing table and a holder to hold the wafer face down against the rotating pad. A slurry containing abrasive and chemical additives are dispensed onto the polishing pad. The pad itself is typically chosen for its ability to act as a carrier of the slurry and to wipe away the grit and debris resulting from the polishing action.
The wafer and polishing pad rotate relative to each other. The rotating action along with the abrasive and chemical additives of the slurry results in a polishing action that removes material from the surface of the wafer. Protrusions on the surface erode more efficiently than recessed areas leading to a flattening or planarization of the wafer surface.
A key factor in maintaining the performance and longevity of the CMP apparatus is conditioning the polishing pad. Typically, the polishing pad is comprised of blown polyurethane with a felt surface layer containing many small pores to facilitate the flow of slurry to beneath the wafer being polished. There are tiny fingers of polyurethane which are substantially perpendicular to the surface of the polishing pad. An example of such a polishing pad is the model IC-1000 manufactured by the Rodel Corporation, 945 East San Salvador Drive, Scottsdale, Ariz. 85258.
As the number of wafers polished increases, the polishing pad becomes filled with debris formed by the accumulation of chemical reaction products and abrasives from the slurry. This causes the polishing pad to become matted down or to wear unevenly, also known as the "glazing effect". Thus, it becomes necessary to restore the polishing pad to a state suitable for continued wafer polishing.
The prior art is replete with methods and apparatus used to condition polishing pads. However, almost all the techniques suffer from being cumbersome or complex. The complicated nature of IC manufacturing requires specialized, high cost equipment in terms of price and subsequent operation and maintenance. Therefore, it is a great advantage to having a simple, low cost, low maintenance polishing pad conditioning technique.
Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide a simple, low cost, low maintenance polishing pad conditioner.
It is another object of the present invention to provide an apparatus for in-situ conditioning and cleaning of a polishing pad.
A further object of the invention is to provide a non-motorized, self-propelling polishing pad conditioner and cleaner.
It is yet another object of the present invention to provide a method of conditioning and cleaning a polishing pad while simultaneously polishing a silicon wafer.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.